This application is a revised R01 proposal that has the general goal of dissecting the importance of various structural domains of the epidermal growth factor (EGF) receptor using mutational analyses. The EGF receptor is a member of a family of protein-tyrosine kinases, termed the type 1 receptor protein kinase subfamily, and is critical for the initiation and control of cellular growth. One consideration in examining EGF-mediated signal transduction that the applicant wishes to address is the extent to which other members of the type 1 receptor protein- tyrosine kinase subfamily, or members of the non-receptor Src family tyrosine kinases, contribute to either the diversity or amplification of signals initiated through the EGF receptor. In this regard, the investigator has recently demonstrated that a kinase-inactive mutant of the EGF receptor can stimulate DNA synthesis. This information, together with previous studies demonstrating that EGF receptor autophosphorylation sites are dispensable for certain mitogenic responses, suggests there exists an EGF receptor-mediated mechanism that can lead to DNA synthesis that may be redundant to and independent of receptor autophosphorylation and/or intrinsic kinase activity. The focus of this application is to elucidate these potential alternative mechanisms and to delineate the structural determinants by which kinase-negative EGF receptors are able to evoke cellular signals. Accordingly, the following Specific Aims are proposed: 1) To generate a panel of kinase-negative EGF receptor mutants in an effort to distinguish receptor structural properties that are necessary for interaction with effector pathways that are crucial for stimulating DNA synthesis independent of EGF receptor kinase activity. 2) To evaluate the role played by ErbB2 in the stimulation of DNA synthesis by kinase- negative EGF receptors. 3) To investigate the participation of Src family kinases in the stimulation of DNA synthesis by kinase-negative EGF receptors.